Conventionally, drowsiness detection by various methods is proposed, for the purpose of preventing the drowsy driving of the vehicle. For example, the driver's face is captured by a camera in the vehicle, and the facial image of the driver is processed for detecting the drowsiness. Such an apparatus is disclosed in, for example, a Japanese patent document JP-A-2008-220424 (also available as a US patent document 20080218359).
The apparatus in the above document determines the eye opening degree and the eyebrow rising. By detecting the eye opening degree, the drowsiness can be detected, because the eye gradually closes as the drowsiness increases. Further, if the driver is in a situation such that he/she is currently driving a vehicle, the driver needs to resist the drowsiness, and thus struggles with the drowsiness by raising the eyebrow in an attempt to overcome the drowsiness. Therefore, by detecting the eyebrow rising, the drowsiness can also be detected.
The eyebrow rising for resisting the drowsiness is different person to person. That is, some people raise only the inner corners of the eyebrows, while other people raise only the outer corners of the eyebrows. Therefore, the rise of the eyebrow cannot be accurately detected, if only the center point of the eyebrow is measured for detecting the drowsiness of the driver who raises inner/outer eyebrow corners only.
In other words, the eyebrow rising detected only by the single point cannot yield an accurate detection result depending on the detection subject, thereby leading to a false detection of drowsiness.